The objectives of this research project will be to quantify and characterize specific cell-surface antigens during preimplantation development of the mouse and to investigate their possible developmental roled. Three antisera (anti-blastocyst serum, anti-placenta serum, anti-teratocarcinoma serum) developed and characterized on mouse embryos in my lab will be used. Experiments fall into four major categories: (1) the quantification of the expression of embryonic surface antigens, (2) the biochemical characterization of these antigens and an analysis of the cross-reactivity of the sera by SDS-polyacrylamide gel electrophoresis and autoradiography, (3) the examination of the effects of monovalent-Fab fragments on adhesion, differentiation and cleavage, (4) the investigation of possible antigenic differences between cells of the ICM and trophoblast cells and the examination of earlier stages to determine when antigenic differences first arise. The information gained will aid in understanding mammalian development and developmental defects, and is of potential value for new approaches to contraception.